The Attenuation of 14-Mev Neutrons from a Point Source Embedded in Concrete Shields

Measurements have been made of the thermal neutron fluxes at various distances from a point source of 14-MeV neutrons embedded in three large shields. The first shield consisted of a 24-m³ assembly of solid concrete building blocks of density 2.2 g/cm³ and gave an attenuation length of 14.1 ± 0.7 cm at a distance of 150 cm from the source. The second shield was a layered assembly of wood and concrete blocks with a mean density of 1.92 g/cm³ and gave an attenuation length of 15.7 ± 0.7 cm at the same distance. The third assembly consisted of a cube of side 61 cm of steel surrounded by concrete blocks; at a distance of 120 cm from the source it gave an attenuation length of 9.3 ± 0.4 cm.